This thesis was originally submitted for examination in March 1983. Following the result of the viva in October of that year an appeal was lodged, and the subsequent proceedings lasted for almost four years. In October 1987 formal notification was made that the thesis could be revised and resubmitted. The prolonged length of the appeal proceedings has meant that the computing environment within which the research was set has developed significantly from the position in 1983. Indeed, in purely practical terms, the computing systems which were used at that time are no longer operational. The opportunity for making modifications and refinements to the record linkage system, and for incorporating additional primary source materials (even were sufficient human resources available), has therefore been removed. Under these circumstances, the record linkage strategies described in the revised thesis are precisely the same as those presented in the 1983 submission. For this reason and because of the extensive delays in carrying out the appeal proceedings it has not seemed appropriate to provide a full review of developments in the record linkage field beyond this date. Reference has, however, been made to the subsequent, crucial impact of the findings of the present research on the progress of the later phases of the 1851 Census National Sample Project, which I co-directed with Professor Michael Anderson at the University of Edinburgh. The entire conceptual and strategic approach to the organisation of family information in this project grew directly from perceptions which were central to the present research. Reference has also been made to the influence of the present research on the development of the SASPAC package, a computing system for handling the 1981 Population Census Small Area Statistics data for Great Britain. I was the chief systems designer of SASPAC, and the design and implementation methods which were adopted in this development drew heavily on the experience gained from the present research. Finally, the opportunity has been taken (in the new Section 10.2), to present the findings of some fresh analyses of 1851 household census data which serve to confirm the validity of the linkage strategies which have been developed.

Transformer ageing is inevitable and it is a challenge for utilities to manage a large fleet of ageing transformers. This means the need for monitoring transformer condition. One of the most widely used methods is oil sampling and testing. Databases of oil test records hence manifest as a great source of information for facilitating transformer ageing assessment and asset management. In this work, databases from three UK utilities including about 4,600 transformers and 65,000 oil test entries were processed, cleaned and analysed. The procedures used could help asset managers in how to approach databases, such as the need for addressing oil contamination, measurement procedure change and oil treatment discontinuities. An early degradation phenomenon was detected in multiple databases/utilities, which was investigated and found to be caused by the adoption of hydrotreatment oil refining technique in the late 1980s. Asset managers may need to monitor more frequently the affected units and restructure long term plans. The work subsequently focused on population analyses which indicated higher voltage transformers (275 kV and 400 kV) are tested more frequently and for more parameters compared with lower voltage units (33 kV and 132 kV). Acidity is the parameter that shows the highest correlation with transformer in-service age. In addition, the influence of the length of oil test records on population ageing trends was studied. It is found that it is possible to have a representative population ageing trend even with a short period (e.g. two years) of oil test results if the transformer age profile is representative of the whole transformer population. Leading from population analyses, seasonal influence on moisture was investigated which implies the importance of incorporating oil sampling temperature for better interpretation of moisture as well as indirectly breakdown voltage records. A condition mismatch between dielectric dissipation factor and resistivity was also discovered which could mean the need for revising the current IEC 60422 oil maintenance guide. Finally, insulation condition ranking was performed through principal component analysis (PCA) and analytic hierarchy process (AHP). These two techniques were demonstrated to be not just capable alternatives to traditional empirical formula but also allow fast, objective interpretation in PCA case, as well as flexible and comprehensive (objective and subjective incorporations) analysis in AHP case.